Trimellitic acid (1,2,4-benzene tricarboxylic acid) although known for some time, has only become commercially available in recent years in the form of its intra-molecular anhydride, trimellitic anhydride, which also may be named 4-carboxyphthalic anhydride. Interest in this trifunctional acid and its simple or monomolecular anhydride has been mainly in the preparation of simple triesters, for example trimethyl, triethyl, triesters from primary C.sub.6 and C.sub.8 oxo-alcohols and trialkyl esters among related simple esters; poly-(amide-imides) resin mainly from diamines which are aromatic in nature; and polyesters related to alkyd resins wherein alkyd forming diols and triols are used with modification by oil-type fatty acids, mono- and di-basic acids to obtain oil or water base surface coating compositions.
Little attention, other than to simple esters as synthetic oils, has been publicized for the potential use of trimellitic acid or its simple anhydride as a building block for the preparation of derivatives soluble in mineral oil, such as the mineral lubricant oils, which would provide addition agents therefor to improve the lubricant oil in service use. It may well be that potential lubricant oil addition agents have been prepared from trimellitic acid or its simple anhydride and have been found to be unsuccessful for the intended additive purpose and, like other unsuccessful research, gone unpublished. Such lack of success may well have come about by the unusual reactivity of the simple anhydride of trimellitic acid. Each of the three carboxyl groups of trimellitic acid have substantially the same reactivity. But the 4-carboxyl group of the simple anhydride is somewhat less reactive than the carboxyl equivalents of the anhydride ring.
That different reactivity makes difficult the introduction of a variety of groups by way of varying carboxyl group modification to introduce two or more new and different functional groups. Also the trifunctionality of trimellitic acid and its simple anhydride is available to cause cross-linking which, although leading to high molecular weight end products with new and varied functional groups, also leads to gel or resin formation not generally desirable for lubricant oil addition agents.
We have discovered a novel class of compounds which are derivatives of trimellitic acid and are soluble in mineral oil. Some members of this class are detergent-dispersant addition agents and hence are useful in the formation of crankcase lubricant oils. Other members of this class, while not meeting present day requirements for detergency-dispersancy function in crankcase lubricant oils, are oil soluble and provide anti-wear or anti-rust or synthetic oil addition agents useful in the formulation of crankcase lubricant oils, or greases or other lubricants where those additive functions are needed.